The present invention relates to an Automatic Gain Control (AGC) circuit, and specifically to an AGC circuit which compensates receiving sensitivity on the part of a subscriber depending on the line status of a central office line (C.O.L) in a private branch exchange(PBX).
In the PBX system, it becomes necessary to improve performance of the PBX by upgrading sensitivity of the central office line through adjusting sensitivity based on the status changes of the central office lines in a trunk circuit.
To achieve the upgrade of the sensitivity, in a conventional method, the AGC circuit adopts digital scheme and is designated in such a way that additional gain memory devices are installed in the PBX of the time division multiplexing type and then the gain memory devices are selected by software-control, otherwise, another way with the use of transistors in a trunk circuit is adopted; therefore, relative commands have to be given from the outside.